1. Field of the Invention
This invention relates to a junction-type field effect transistor and more particularly to a method of manufacturing a junction type field effect transistor having vertical structure.
2. Description of the Prior Art
Vertical structure junction type field effect transistors (referred to as VSJFET hereinbelow) are suited for the purpose of obtaining a large drain current, i.e. for high output power use, compared to the lateral structure FET's. This is because the gate region in a VSJFET can be formed in geometrically divided multiple regions which enables a large current flow in total. Such a VSJFET is, for example, shown in Japanese Pat. Publication No. 41478/1972. FIGS. 1A to 1E show the conventional steps of manufacturing a VSJFET which will be described hereinbelow.
On a p.sup.+-type silicon substrate 1, a p-type silicon layer 2 is grown by the epitaxial growth method (FIG. 1A). An n-type impurity is selectively diffused into the p-type silicon layer 2 to form a multiplicity of n-type gate regions 3 leaving the p-type channel regions (FIG. 1B). Then, a p-type silicon layer 4 is epitaxially grown on the p-type silicon layer 2 including the n-type gate regions 3 (FIG. 1C). An n-type impurity is doped into desired portions of the p-type layer 4 to form gate extension regions 5 registered with desired portions of the gate regions 3 for forming a gate electrode (FIG. 1D). A p-type impurity is diffused in a desired portion of the p-type silicon layer 4 to form a p.sup.+-type source region 6 (FIG. 1E).
According to the above process, however, in the step of FIG. 1C the n-type impurity doped preliminarily in the n-type region 3 causes out-diffusion into the p-type layer 4 and forms an extended layer 2A, resulting in reduction of the breakdown voltage between the gate region and the source region. Further, due to this out-diffusion phenomenon, the gate length G.sub.l of the JFET increases (FIG. 1C) resulting in increase of the series resistance R.sub.S of the channel region and hence increase of power loss